In an attempt to prevent restenosis, metallic vascular stents have been permanently implanted in coronary or peripheral vasculature. These stents are typically delivered intraluminally by a catheter and expanded in place to support a diseased portion of an artery.
One shortcoming of these conventional stents is that even after stent implantation, restenosis can still occur. Another shortcoming is that during the implantation of the stent, the stent may cause particles to discharge from the artery wall through the open cell. These dislodged particles can embolize in the bloodstream, and may cause catastrophic effects.
In an attempt to reduce these problems, coverings have been proposed for stents. These coverings have been made from artificial materials, such as PTFE. As of yet, however, coverings made from artificial materials have not proven successful. This may be because of the poor biocompatibility of such materials.
There is also some experience using biological tissue such as bovine pericardium to build a covering for a stent that is more biocompatible than coverings made from artificial materials. Preliminary results with bovine pericardium have been encouraging from the point of view of biocompatibility.
The current method, however, of creating a covering using biological tissue is simplistic. A rectangular piece of pericardium is harvested from a bovine source. The pericardium is then, after being prepared so that it is suitable for implantation, rolled into a cylinder. The abutting edges of the pericardium are sewn together to create a covering. This covering is then placed over a stent.
There is an inherent disadvantage in this cut and sew approach to creating a covering. Biological tissue has a very small expansion range. Therefore, the diameter of the cut and sewn cylinder of tissue is limited to a very small range. This limits the stent to a very small range of expansion diameters, limiting the utility of the stent. This also limits the difference in diameter between the stent as delivered and the stent at its expanded state, increasing significantly the profile of the delivery system required for a given supported diameter.